Process for Producing Carboxylic Acid Anhydrides

ABSTRACT

The present invention relates to a process for producing carboxylic acid anhydrides by the carbonylation reaction of a carboxylic acid ester, derived from an alcohol and a carboxylic acid, with carbon monoxide containing a small amount of hydrogen in a liquid reaction medium in the presence of a Group VIII B catalyst to produce a carboxylic acid anhydride. The liquid reaction medium comprises the Group VIII B catalyst, an organic halide, the carboxylic acid ester, an alkali metal salt, the carboxylic acid anhydride, the carboxylic acid, N-acetylimidazole as a protecting agent, and ethylidene diacetate (EDA) as an organic promoter. By making use of the protecting agent of N-acetylimidazole, metal ions in the reactor can be prevented from reacting with EDA so as to reduce the formation of hardly-soluble tars during the reaction. Also, the EDA organic promoter is kept at a certain content in the system to promote the overall carbonylation reaction rate.

FIELD OF THE INVENTION

The present invention relates to a process for producing carboxylic acidanhydrides by the carbonylation reaction of a derivative from an alcoholand a carboxylic acid with carbon monoxide, and in particular, a processfor producing acetic anhydride by the carbonylation reaction of methylacetate with carbon monoxide.

BACKGROUND TO THE INVENTION

Acetic anhydride, a well-known raw material widely used in the chemicalindustry, is mainly used to produce chemicals such as cellulose acetateand is an important raw material for synthesis of medicines, flavors,dyes, etc. There are currently three industrial processes for producingacetic anhydride, including the ketene process, the acetaldehydeoxidation process and the methyl acetate carbonylation process. Amongthese, the predominant is the ketene process, which is an old-fashionedand small-scale process and is adopted by many manufacturers; however,due to its high energy consuming and other drawbacks, the largestcommercial scale production of acetic anhydride is currently the methylacetate carbonylation process.

The ketene process is carried out by dissociating one water molecule ormethane from the raw material of acetic acid or acetone at a hightemperature to form ketene, which then reacts with acetic acid to formacetic anhydride. This process, which must be carried out at a reactiontemperature of up to 750° C., will gradually go out of use in the futuredue to its high energy-consuming demand.

The acetaldehyde oxidation process makes use of the metal catalyst suchas Mn, Co, Ni, Cu, etc. to oxidize acetaldehyde into peracetic acid,which further reacts with acetaldehyde to form acetic anhydride and aby-product of water. Acetic anhydride will further be hydrolyzed intoacetic acid; that is, the final product will be the mixture of aceticanhydride and acetic acid. Therefore, the yield of acetic anhydride willbe decreased.

The methyl acetate carbonylation process for producing acetic anhydrideis an expanded application of the methanol carbonylation process forproducing acetic acid and makes use of methyl acetate and carbonmonoxide as the raw materials to produce acetic anhydride in thepresence of transition metal catalysts (such as Rh, Ni, Co and Ir)andiodidepromoter. The difference between the methyl acetatecarbonylation process for producing acetic anhydride and the methanolcarbonylation process for producing acetic acid is the water content ofthe reaction solution; the reaction solution of the former has to bekept in anhydrous conditions, while the reaction solution of the lattercan have 1 to 20 wt. % of water content. Water has a great influence onthe stability of the catalyst, and the high water content can facilitatethe stability of the catalyst. Therefore, the stability of the catalystin the anhydrous system of the methyl acetate carbonylation process is aprimary problem that should be overcome. To solve the problem, apromoter or a co-catalyst such as alkali metal, phosphonium salt,ammonium salt and transition metal catalysts can be added to promote thestability and activity of the catalytic system. In addition, in themethyl acetate carbonylation process for producing acetic anhydride, asmall amount of hydrogen must be added in the carbon monoxide feed gasto maintain the activity of the Rh catalyst.

Adding one or more promoters into the catalytic system to improve andpromote the catalytic efficiency of the catalyst is the most importantsubject in these researches. U.S. Pat. No. 4,002,678 discloses thatunder an anhydrous condition, a carbonylation reaction is carried out byusing nickel and chromium as the catalyst and carbon monoxide and methylacetate or dimethyl ether as the raw materials in the presence of ahalide and a trivalent organo-nitrogen compound or a trivalentorgano-phosphorus compound. European Pub. No. 0391680 A1 discloses aprocess for preparing a carboxylic acid by using an alcohol or its esterunder a water-containing condition, in which a quaternary ammoniumiodide is used as a stabiliser of the rhodium catalyst. U.S. Pat. No.4,115,444 discloses a process for preparing acetic anhydride, in which aGroup VIIIB noble metal is used as the catalyst, together with multiplepromoters comprising at least one metal of Groups IVB, VB, and VIB or anon-noble metal of Group VIIIB, or their compounds and a trivalentorgano-nitrogen compound or a trivalent organo-phosphorus compound; thecatalyst thereof is rhodium and iridium, the metal promoter is iron,cobalt, nickel, chromium, etc., and the organo-nitrogen compoundpromoter includes an amine, an imidazole, an imide, an amide, an oxime,etc. China Pub. Nos. 1876239 A and 1778468 A both disclose a catalyticsystem for synthesis of the carbonyl group of methyl acetate to an acidanhydride, in which a Rh compound is used as the catalyst and differentamounts of alkyl iodides, hetero-polyacid salts and alkali metal iodinesalts are used as the promoter; the performance of this catalytic systemcan be improved by the synergistic effect of the hetero-polyacid saltsand the catalyst. U.S. Pat. No. 7,553,991 discloses that making use ofdifferent nitrogen-containing heterocyclic organic promoters in thecarbonylation process to form with the Rh catalyst a stabilized complexcan increase the carbonylation reaction rate, and adding such kind oforganic promoter can lower the reaction temperature or keep the originalreaction rate with a reduced LiI amount, which has the effect of savingenergy and reducing production cost. Both U.S. Pat. Nos. 5,298,586 and4,430,273 clearly disclose that in the Rh-catalyzed carbonylationprocess for producing carboxylic acid anhydride under anhydrousconditions, adding ionic iodides containing quaternary nitrogen caneffectively improve the stability and solubility of the Rh catalyst.Taiwan Patent Application No. 097147075 discloses that adding an ionicliquid containing cations having a nitrogen-containing heterocyclicstructure in the carbonylation process can increase the carbonylationreaction rate, and the ionic liquid is easily separated and recoveredfrom the catalytic system due to its features such as thermal stability,chemical stability and low vapor pressure.

In the industrial methyl acetate carbonylation process for synthesizingacetic anhydride, a noble metal and iodide catalytic system is generallyused. However, such a system usually produces hardly-soluble tars duringthe carbonylation process. Cao Yu, et al. of Shanghai Coking & ChemicalCorp. had a research on the tar components in carbonylation synthesisfor acetic anhydride and investigated the reaction mechanism of tarformation [Shanghai Chemical Industry, 2006, Vol. 31, Issue 07]. It wasfound that in a continuous carbonylation process, by-products such asacetaldehyde, vinyl acetate, ethylidene diacetate, etc. will be formedat the same time, and these by-products tend to react with the metalions, especially noble metal ions, in the reactor and formhardly-soluble tars. Because the tar will reduce the activity of thecatalyst and even encapsulate the iodides and noble metal catalyst todeactivate the catalyst and terminate the carbonylation reaction,lowering the carbonylation reaction rate, the control of tar formationis one of the key points for improving the carbonylation process.

As mentioned in many prior art patents, the formation of tar residuesoccurs in the carbonylation process of esters and ethers for producingacetic anhydride and ethylidene diacetate, and the tar residues tend toencapsulate the metal Rh and damage the Rh catalyst. Therefore, currentpatented technologies all focus on the method of removing the tarresidues and recycling and reusing the Rh catalyst. The Rh recyclingtechnologies can roughly classified into the extraction method, theprecipitation method, the combustion method and the adsorptionseparation method. U.S. Pat. Nos. 4,340,569, 4,340,570 and 4,341,741 alldisclose the noble metal, including rhodium, can be recycled bypretreatment with an alcohol, concentration via evaporation, treatmentwith an amine, and then extraction with hydrogen halide. Canada Pat. No.1171879 discloses extraction of noble metals, including rhodium, withsolvents which preferentially dissolve the tars; such solvents includealkanes, cycloalkanes, halogenated alkanes, and aromatic hydrocarbons,and particularly cyclohexane, toluene, and carbon tetrachloride. U.S.Pat. No. 3,920,449 discloses recycling the metal Rh by pyrolysis of theresidues. U.S. Pat. No. 3,978,148 discloses recycling the metal Rh byadsorption of the metal Rh on the active carbon. U.S. Pat. No. 3,560,539discloses making use of hydrogen and hydrides to reduce the formation ofhydroxyl group from the carbonyl group in the tar, so as to release andthus recycle the Rh complex.

Therefore, it is still a main challenge in the future to develop a moreeconomic process that can effectively prolong the life of Rh catalyst,reduce the tar formation, lower the complexity of the process andincrease the space-time yield of carboxylic acid anhydrides at the sametime.

SUMMARY OF THE INVENTION

The main object of the present invention is to provide a process forproducing carboxylic acid anhydrides, which can keep a high reactionrate and reduce the tar formation under anhydrous conditions.

In order to achieve the aforementioned and other objects, the processfor producing carboxylic acid anhydrides according to the presentinvention is carried out by the carbonylation reaction of a carboxylicacid ester, derived from an alcohol and a carboxylic acid, with carbonmonoxide containing a small amount of hydrogen in a liquid reactionmedium in the presence of a Group VIII B catalyst to produce acarboxylic acid anhydride.

The reaction medium mainly comprises a Group VIII B catalyst, an organichalide, a carboxylic acid ester, an alkali metal salt, ethylidenediacetate (EDA) as an organic promoter, N-acetylimidazole as aprotecting agent, a carboxylic acid anhydride, a carboxylic acid, and asmall amount of impurities. Specifically, in the liquid reaction medium,300 to 3000 ppm of the Group VIII B catalyst, 5 to 30 wt. % of theorganic halide, 1 to 15 wt. % of the alkali metal salt, 0.5 to 20 wt. %of EDA, 0.5 to 20 wt. % of N-acetylimidazole, and the carboxylic acidester, the carboxylic acid anhydride, the carboxylic acid and the smallamount of impurities are usually contained. The EDA organic promoter hasto be kept at a certain content in the system, and its content can bekept by production from a side reaction of the system or by addition.

As used in the present invention, the alcohol is an aliphatic alcoholcompound having 1 to 6 carbon atoms, the carboxylic acid is a carboxylicacid having 1 to 6 carbon atoms, and the CO gas taking part in thecarbonylation reaction contains an appropriate amount of hydrogen tofacilitate maintaining the catalytic activity. Preferably, the CO feedgas contains hydrogen at a concentration of from 0.1 to 10%. Inaddition, the Group VIII B catalyst is one or more catalysts selectedfrom the group consisting of rhodium, nickel, cobalt and iridium; theorganic halide can be a methyl halide such as, for example, methyliodide; and the alkali metal salt can be a Group IA/IIA iodide salt suchas, for example, lithium iodide, and the liquid reaction medium cancontain 500 to 8000 ppm of Group IA/IIA metal ions to provide thecorresponding content of iodine ions.

According to the present invention, the carbonylation reaction can becarried out at a temperature of from 160 to 240° C. and at aCO-controlled pressure of from 20 to 60 kg/cm².

In the Group VIIIB catalytic system for the carbonylation reaction ofthe present invention, the protecting agent of N-acetylimidazole is usedto reduce the formation of hardly-soluble tars and the EDA organicpromoter is used to increase the space-time yield of carboxylic acidanhydride, so that the operation range of the reaction can be expandedand the reaction can be carried out under milder conditions.

The process for producing carboxylic acid anhydrides according to thepresent invention will be described below in detail with reference tothe following embodiments, and also as set forth in applicants'Taiwanese priority application No. 099129234, filed Aug. 31, 2010, theentire contents of which are hereby incorporated herein by reference.However, these embodiments are used mainly to assist in understandingthe present invention, but not to restrict the scope of the presentinvention. Various possible modifications and alterations could beconceived of by one skilled in the art to the form and the content ofany particular embodiment, without departing from the spirit and scopeof the present invention, which is intended to be defined by theappended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the infrared spectra of Examples 1 to 3.

FIG. 2 shows the infrared spectra of Examples 4 to 6.

DESCRIPTION OF PREFERRED EMBODIMENTS

The features and effects of the present invention will be furtherexplained with reference to the preferred embodiments below, which are,however, not intended to restrict the scope of the present invention.

The present invention can be operated as a batch process, in which theequipment as used mainly includes, for example, a one-liter reactor anda CO storage tank both made of anticorrosive materials. The reactoritself is provided with a speed-change motor capable of controlling therotational speed, which can be appropriately adjusted so as to maintaina vapor/liquid well-mixing effect. The inside and the outside of thereactor are provided with a cooling coil and an electrically heatingplate, respectively, so as to control and maintain a stable reactiontemperature. A pressure control valve is provided between the reactorand the hydrogen and CO storage tanks so as to maintain and control thepressure of the main reactor.

One preferred embodiment of the present invention is to produce aceticanhydride by carrying out the carbonylation reaction of methyl acetatewith carbon monoxide containing a small amount of hydrogen in thereactor. The reaction medium in the reactor for carrying out thecarbonylation reaction is maintained to comprise a Group VIII B catalystsuch as, for example, rhodium; a carboxylic ester derived from analcohol and a carboxylic acid such as, for example, methyl acetate, oran ether derived from an alcohol compound such as, for example, dimethylether; an organic halide corresponding to the raw material of alcohol,such as, for example, methyl iodide; an alkali metal salt such as, forexample, lithium iodide; a carboxylic acid anhydride such as, forexample, acetic anhydride; a carboxylic acid such as, for example,acetic acid; the EDA organic promoter; and the protecting agent ofN-acetylimidazole.

Alternatively, the present invention can be operated as a continuousprocess. Another preferred embodiment of the present invention is tocontinuously feed the raw material of methyl acetate, together withcarbon monoxide containing a small amount of hydrogen, into thecarbonylation reactor and react methyl acetate with carbon monoxide toproduce acetic anhydride. The liquid reaction medium in the reactorcomprises the Rh catalyst, methyl acetate, acetic acid, aceticanhydride, methyl iodide, an alkali metal salt, the EDA organicpromoter, and the protecting agent of N-acetylimidazole. Correspondingto the continuously feeding reactor, the reaction product effluentcomprises the product of acetic anhydride and the unreacted methylacetate, acetic acid, methyl iodide, Rh catalyst, alkali metal salt, theEDA organic promoter, and the protecting agent of N-acetylimidazole. Theliquid reaction product is continuously outputted to a flash tank (or anevaporator), the light constituents of the liquid reaction product areevaporated and discharged from the top of the flash tank to thepurifying zone to further separate acetic acid and acetic anhydride, andthe Rh catalyst and other heavy constituents at the bottom of the flashtank are reflowed to the reactor. After the product of acetic anhydrideis separated in the purifying zone, acetic acid and other constituents(including methyl iodide, methyl acetate, etc.) are reflowed to thereactor. During the reaction process, methyl iodide, the alkali metalsalt and the aforementioned organic promoter and protecting agent willnot be consumed but are continuously circulated from the flash tank orthe purifying zone to the reactor. If necessary, persons skilled in theart can consider adjusting the contents of the constituents of thereaction medium in accordance with the real operation situation.

The following Examples 1 to 6 are used to demonstrate thatN-acetylimidazole can prevent metal ions, especially noble metal ions(for example, the Rh catalyst), from reacting with ethylidene diacetateand thus can reduce the formation of hardly-soluble tars during thereaction.

Example 1

After 0.29 g of ethylidene diacetate, 0.37 g of IrCl₃.XH₂O (in which Iratom accounts for 52.5%) and 100 ml of ethanol were added into areaction flask and heated to 100° C., a reaction was carried out underreflux for 20 hours. The product, after cooled to normal temperature,was filtered to obtain black precipitated solids and a tawny solution.The tawny solution was concentrated, washed with ether, and then driedto remove the solvent. The infrared spectrum of the final product wasdetermined ((a) in FIG. 1) and was taken as a control experiment.

Example 2

After 0.22 g of N-acetylimidazole, 0.37 g of IrCl₃.XH₂O (in which Iratom accounts for 52.5%) and 100 ml of ethanol were added into areaction flask and heated to 100° C., a reaction was carried out underreflux for 20 hours. The product, after cooled to normal temperature,was filtered to obtain yellow solids and a yellow solution. The yellowsolution was concentrated, washed with ether, and then dried to removethe solvent. The infrared spectrum of the final product was determined((b) in FIG. 1) and was taken as a control experiment.

Example 3

After 0.29 g of ethylidene diacetate, 0.22 g of N-acetylimidazole, 0.37g of IrCl₃.XH₂O (in which Ir atom accounts for 52.5%) and 100 ml ofethanol were added into a reaction flask and heated to 100° C., areaction was carried out under reflux for 20 hours. The product, aftercooled to normal temperature, was filtered to obtain yellow solids and ayellow solution. The yellow solution was concentrated, washed withether, and then dried to remove the solvent. The infrared spectrum ofthe final product was determined ((c) in FIG. 1).

By comparing the infrared spectrum of the Example 3 with those of theExamples 1 and 2, it is obvious that the spectrum signal of the Example3 is similar to that of the Example 2; in other words, the coordinationability of N-acetylimidazole with Ir ions is better, which demonstratesthat addition of such kind of protecting agent according to the presentinvention can indeed prevent ethylidene diacetate from reacting with Irions.

Example 4

After 0.29 g of ethylidene diacetate, 0.27 g of RhCl₃.XH₂O (in which Rhatom accounts for 38%) and 100 ml of ethanol were added into a reactionflask and heated to 100° C., a reaction was carried out under reflux for20 hours. The product, after cooled to normal temperature, was filteredto obtain black precipitated solids and a light yellow solution. Thelight yellow solution was concentrated, washed with ether, and thendried to remove the solvent. The infrared spectrum of the final productwas determined ((a) in FIG. 2) and was taken as a control experiment.

Example 5

After 0.22 g of N-acetylimidazole, 0.27 g of RhCl₃.XH₂O (in which Rhatom accounts for 38%) and 100 ml of ethanol were added into a reactionflask and heated to 100° C., a reaction was carried out under reflux for20 hours. The product, after cooled to normal temperature, was filteredto obtain a small amount of black precipitated solids and a redsolution. The red solution was concentrated, washed with ether, and thendried to remove the solvent. The infrared spectrum of the final productwas determined ((b) in FIG. 2) and was taken as a control experiment.

Example 6

After 0.29 g of ethylidene diacetate, 0.22 g of N-acetylimidazole, 0.27g of RhCl₃.XH₂O (in which Rh atom accounts for 38%) and 100 ml ofethanol were added into a reaction flask and heated to 100° C., areaction was carried out under reflux for 20 hours. The product, aftercooled to normal temperature, was filtered to obtain a small amount ofblack precipitated solids and a red solution. The red solution wasconcentrated, washed with ether, and then dried to remove the solvent.The infrared spectrum of the final product was determined ((c) in FIG.2).

By comparing the infrared spectrum of the Example 6 with those of theExamples 4 and 5, it is obvious that the spectrum signal of the Example6 is similar to that of the Example 5; in other words, the coordinationability of N-acetylimidazole with Rh ions is better, which demonstratesthat addition of such kind of protecting agent according to the presentinvention can indeed prevent ethylidene diacetate from reacting with Rhions.

The following Comparative Example 1 and Examples 7 to 15 are used todemonstrate that the EDA organic promoter present in the system at acertain amount will facilitate increasing the space-time yield of aceticanhydride.

Comparative Example 1

In this comparative example, a batch process without adding the organicpromoter of the present invention was used, as a comparative experiment,to carry out the carbonylation reaction. The amount of each constituentfed into the reactor was: 43 wt. % of methyl acetate, 18 wt. % of methyliodide, 18 wt. % of acetic anhydride, lithium iodide (4000 ppm of Liion), 1400 ppm of the Rh catalyst, and an appropriately balanced amountof acetic acid as a solvent. The reactor into which the mixture of theaforementioned reactants had been fed was firstly pressurized withhydrogen to 1 kg/cm², and then carbon monoxide was introduced into thereactor, followed by a gradual elevation of temperature. After the settemperature for the reaction was reached, carbon monoxide was resuppliedso that the inner pressure of the system reached 27 kg/cm². During thereaction, carbon monoxide kept on being resupplied with its consumptionso that the pressure stably maintained 27 kg/cm². The amount of COconsumption was recorded and sampling was conducted for analysis tocalculate the unit space-time yield (STY) of acetic anhydride (unit:mole/liter*hour).

Examples 7-9 Influence of Addition of Organic Promoter on Reaction Rate

The carbonylation reactions were carried out under the same conditionsas the Comparative Example 1, except that 1 wt. %, 3 wt. % and 5 wt. %of the EDA organic promoter were added in the initial reaction media,respectively. The results of the Examples 7-9 and the ComparativeExample 1 were recorded in Table 1 where the Comparative Example 1 was ablank experiment that no EDA organic promoter was added. It is obviousfrom Table 1 that the STY values of the carbonylation reaction withdifferent amounts of the EDA organic promoter added were all increasedby different levels and reached at least 7 gmol/L*h or above, whichshows the addition of such kind of organic promoter according to thepresent invention can indeed increase the unit space-time yield ofacetic anhydride.

TABLE 1 Influence of addition of organic promoter on reaction rate Pres-LiI STY Amount of EDA added Temp. sure (Kg/ (Li (gmol/ Reagent (wt. %)(° C.) cm²) ppm) L*hr) CEx. 1 — — 190 27 4000 6.40 Ex. 7 EDA 1 190 274000 7.04 Ex. 8 3 190 27 4000 7.25 Ex. 9 5 190 27 4000 7.04

Examples 10-13 Influence of Reaction Temperature and Organic Promoter onReaction Rate

The carbonylation reactions were carried out under the same conditionsas the Comparative Example 1, except that 3 wt. % of the EDA organicpromoter was added in the initial reaction media and the reactiontemperature was changed. The results were recorded in Table 2. It isobvious from Table 2 that the STY values of the carbonylation reactioncan still be increased by adding the organic promoter and changing thereaction temperature, which shows the addition of such kind of organicpromoter under different reaction temperatures according to the presentinvention can indeed increase the yield of acetic anhydride. Also, fromthe comparison between the Examples 10 and 11 and the ComparativeExample 1, adding such kind of organic promoter can have a betterreaction rate at a lowered reaction temperature, which is energy-savingand can lower the production cost.

TABLE 2 Influence of reaction temperature and organic promoter onreaction rate Pres- LiI STY Amount of EDA added Temp. sure (Kg/ (Li(gmol/ Reagent (wt. %) (° C.) cm²) ppm) L*hr) CEx. 1 — — 190 27 40006.40 Ex. 8 EDA 3 190 27 4000 7.25 Ex. 10 3 180 27 4000 6.85 Ex. 11 3 18527 4000 7.02 Ex. 12 3 195 27 4000 7.25 Ex. 13 3 200 27 4000 7.48

Examples 14-15 Influence of Reaction Pressure and Organic Promoter onReaction Rate

The carbonylation reactions were carried out under the same conditionsas the Comparative Example 1, except that 3 wt. % of the EDA organicpromoter was added in the initial reaction media and the reactionpressure was changed. The results were recorded in Table 3. It isobvious from Table 3 that the STY values of the carbonylation reactioncan indeed be increased by adding the organic promoter and increasingthe reaction pressure, which shows the addition of such kind of organicpromoter under different reaction pressures according to the presentinvention can indeed increase the yield of acetic anhydride.

TABLE 3 Influence of reaction pressure and organic promoter on reactionrate Pres- LiI STY Amount of EDA added Temp. sure (Kg/ (Li (gmol/Reagent (wt. %) (° C.) cm²) ppm) L*hr) CEx. 1 — — 190 27 4000 6.40 Ex. 8EDA 3 190 27 4000 7.25 Ex. 14 3 190 24 4000 7.24 Ex. 15 3 190 30 40007.48

What is claimed is:
 1. A process for producing carboxylic acidanhydrides by the carbonylation reaction of a carboxylic acid ester,derived from an alcohol and a carboxylic acid, with carbon monoxidecontaining a small amount of hydrogen in a liquid reaction medium in thepresence of a Group VIII B catalyst to produce a carboxylic acidanhydride, the reaction medium comprising the Group VIII B catalyst, anorganic halide, the carboxylic acid ester, an alkali metal salt, thecarboxylic acid anhydride, the carboxylic acid, N-acetylimidazole as aprotecting agent, and ethylidene diacetate (EDA) as an organic promoter,wherein the content of the organic promoter in the reaction system canbe kept by producing the organic promoter from a side reaction or byfurther adding the organic promoter into the reaction system.
 2. Theprocess according to claim 1, wherein the alcohol is an alcohol having 1to 6 carbon atoms.
 3. The process according to claim 1, wherein thecarboxylic acid is a carboxylic acid having 1 to 6 carbon atoms.
 4. Theprocess according to claim 1, wherein the carboxylic acid ester ismethyl acetate.
 5. The process according to claim 1, wherein thecarboxylic acid is acetic acid.
 6. The process according to claim 1,wherein the carboxylic acid anhydride is acetic anhydride.
 7. Theprocess according to claim 1, wherein the carbonylation reaction iscarried out at a temperature of from 160 to 240° C.
 8. The processaccording to claim 1, wherein the carbonylation reaction is carried outat a pressure of from 20 to 60 kg/cm².
 9. The process according to claim1, wherein the reaction medium contains the Group VIII B catalyst at atotal concentration of from 300 to 3000 ppm.
 10. The process accordingto claim 1, wherein the Group VIII B catalyst is one or more catalystsselected from the group consisting of rhodium, nickel, cobalt andiridium.
 11. The process according to claim 1, wherein the organichalide is a methyl halide.
 12. The process according to claim 11,wherein the methyl halide is methyl iodide.
 13. The process according toclaim 1, wherein the reaction medium contains 5 to 30 wt. % of organichalide.
 14. The process according to claim 1, wherein the carbonmonoxide feed gas contains hydrogen at a concentration of from 0.1 to10%.
 15. The process according to claim 1, wherein the alkali metal saltis a Group IA/IIA iodide salt.
 16. The process according to claim 15,wherein the reaction medium contains 500 to 8000 ppm of Group IA/IIAmetal ions to provide the corresponding content of iodine ions.
 17. Theprocess according to claim 1, wherein the content of the organicpromoter of ethylidene diacetate is kept at 0.5 to 20 wt. %.
 18. Theprocess according to claim 1, wherein the protecting agent ofN-acetylimidazole is added at a content of 0.5 to 20 wt. %.